The present invention relates to a method for manufacturing an electrode supporting base plate for a radiation detector used in a tomography device.
A device called a computerized tomography device (to be referred to as a CT device hereinafter for brevity) as a tomography device is known. In a CT device of this type, as shown in FIG. 1, an X-ray source 1 for radiating in a pulsed manner a divergent X-ray beam FX extending in the form of a flat circular section opposes, through a subject 3, a radiation detector 2 having an array of radiation detecting cells for detecting the X-ray beam FX. The radiation detector 2 collects X-ray absorption data in various directions with respect to the subject 3 by rotating the X-ray source 1 and the radiation detector 2 in synchronism in the same direction about the subject 3.
After collecting sufficient data, this data is analyzed with a computer to calculate the X-ray absorption ratios at individual positions with respect to the subject. Then, the scanning section of the subject is reconstituted with a gradation corresponding to the absorption ratios. Since the analysis may be accomplished with a gradation of as many as 2,000 steps according to the composition, a desired tomography image of soft to hard tissue may be obtained.
For collection of the X-ray absorption data, the radiation detector 2 detects by A-D conversion the ionizing current from the X-ray energy which has been transmitted through the subject 3 along a line (to be referred to as an X-ray path) connecting the X-ray source 1 and the respective radiation detecting cells forming an ionization chamber. The detected energy is discharged by a discharging ciurcuit of a predetermined time constant and this discharging time is obtained as the X-ray absorption data.
The resolution therefore depends upon the number of radiation detecting cells constituting the radiation detector per unit length along the direction of their arrangement, and also on the precision (the width of the electrodes and the pitch of their arrangement). In general, the radiation detecting cells are capable of simultaneously obtaining several hundred pieces of X-ray absorption data. As shown in FIG. 1, the radiation detecting cells are arranged parallel to the X-ray path in an arc-shaped box with the X-ray source being positioned at the center of the arc. Xenon gas or the like is sealed within the box. Thus, as shown in FIG. 2, high-voltage electrodes 22 and signal absorption electrodes 23 are alternately arranged in a box body 2 with a predetermined spacing therebetween to be parallel to the respective X-ray paths of the X-ray beam FX, and radiation detecting cells 20 are formed between these electrodes.
As has been described earlier, the CT device calculates the composition of the scanning section from the positional relationship between the opposing X-ray source and the radiation detector and from the X-ray absorption of the X-ray absorbing material interposed therebetween. Therefore, correct X-ray absorption data may not be obtained if the position precision of the pitch of the high-voltage electrodes 22 and the signal absorption electrodes 23 is not high.
The radiation detector usually constitutes several hundred radiation detecting cells in order to increase the data within the limited divergent beam for higher spatial position resolution. Since the spacing between the respective electrodes 22 and 23 constituting the radiation detecting cells is as short as several hundred microns, advanced techniques are required to keep the mechanical precision of the electrode inserting grooves high.
According to the current technique which is usually adopted, as shown in FIG. 3, an electrode supporting base plate is used which is obtained by forming with a machine tool or the like grooves 24a of a predetermined spacing in an insulator 24 of plate shape and made of ceramic or the like. Two such electrode supporting base plates are paired in such a manner that their sides with the grooves 24a oppose each other, and the upper and lower ends of the high-voltage electrodes 22 and the signal absorbing electrodes 23 are alternately inserted in the grooves. The parts of the electrodes 22 and 23 inserted in the grooves 24a are adhered with an adhesive 25 such as epoxy resin.
A single block of the electrode supporting base plate may be housed within an arc-shaped box body 21. However, in general, small blocks each containing several tens of electrodes are housed within the box body 21 so that only damaged parts of the structure need be replaced.
The electrode supporting base plate corresponding to one block includes, for example, 100 grooves of 200.mu. width with a pitch of 60.mu. and thus is a product of high density which requires high precision. An error margin of less than 1 to 2.mu. is necessary for the groove width and pitch, and an error greater than this results in a detector which may not be usable. Since generally 26 blocks of the electrode supporting base plate are used for one detector, the manufacture of detectors is extremely difficult and costly due to the problem of processing precision.